This invention relates to a printer which prints information on a continuous form by transferring toner images thereonto, and more particularly to a justification system for controlling printing in accordance with the rules on the continuous form.
Conventionally, there is known an image recording device utilizing a so-called electrophotographic system in which a surface of a photoconductive drum is exposed to light to form a latent image on the drum surface, toner is then applied to the latent image to develop the image, and the developed image is transferred onto a recording sheet material and is fixed by a fixing unit. Such an image recording device is chiefly employed in a copying machine. In recent years, however, image recording devices have been utilized in printers and the like for printing out output from a computer.
In a copying machine, in general, cut sheets are used as the recording sheet material, and a heat-roll fixing system is utilized wherein the toner is fixed by heat as well as pressure. In addition, a pressure fixing system has recently been developed, which is low in electric power consumption and which does not require an undue amount of time for preheating the heat rolls.
In the printer, however, it is desired to use, as the recording material, a continuous recording which is form identical with that used in a conventional line-printer; the continuous recording form identical to the conventional one is a folded continuous recording form (hereinafter referred to simply as "continuous form"), called a fan-folded form, which has formed therein sprocket holes. Perforations are provided between each of the folded sections to enable sheet sections to easily be severed from each other. Horizontal rules are marked at predetermined intervals in a longitudinal direction between the perforations, with a predetermined positional relationship respective to the sprocket holes.
In the above printer, a continuous form having carried thereon unfixed toner image is clamped and passed between a pair of rotating fixing rolls so that the toner image is fixed onto the continuous form. The continuous form is driven to travel by, for instance, rotation of the fixing rolls.
In the meantime, the printer employing the fan-folded form defines a non-printing area around the perforations because the form is cut into pieces of paper at the perforations after printing.
In the printer described above, however, expansion or contraction of the continuous form due to humidity, variation in the diameter of the fixing rolls, change in the thickness of the continuous form at the fixing rolls, and so on, cause printable segments of the continuous form to be out of phase with the associated area of the circumferential peripheral surface of the photoconductive drum, relative to rules.
Further, motors utilized for scanning the photoconductive drum and the exposure system are varied in their rpm (revolutions per minute) due to the variation in supply voltage and their age. Thus, even if each printing segment of the continuous form is fed at a constant rate, the associated area of the photoconductive drum is shifted out of position and thereby the printing position is slipped away from the rules, resulting in a poor impression.
Moreover, the continuation of printing accumulates such errors, making the rules meaningless. In the worst case, the printing occurs at non-printing areas around the perforations.